1. Field of the Invention
The present invention relates to an electrodeionization water producing apparatus used in the semiconductor manufacture industry, pharmaceutical industry, food industry, power stations, laboratories and the like which require deionized water.
2. Description of the Related Art
Basically in a conventional electrodialysis device, the liquid to be treated is desalinated and concentrated by supplying direct currents to a unit in which a plurality of cation and anion exchange membranes are alternately arranged via spacers and desalination and concentrating chambers are formed by the spacers, so that the anion and cation exchange membranes do not contact one another. Moreover, in an electrodeionization water producing apparatus heretofore practically used, a gap formed by the cation and anion exchange membranes is basically filled, for example, with a lamination of anion and cation exchange resin layers or a mixed ion exchange resin layer as an ion exchanger to form a desalination chamber. Feed water is passed through the ion exchange resin layer(s), while direct currents are applied via both ion exchange membranes, so that deionized water is produced while ions in the feed water are electrically discharged to concentrated brine flowing outside both the ion exchange membranes, and the anion and cation exchange membranes do not directly contact each other.
FIG. 5 is a schematic sectional view of a typical conventional electrodeionization water producing apparatus. As shown in FIG. 5, cation exchange membranes 101 and anion exchange membrane 102 are alternately arranged apart from one another, and every other space formed by the cation exchange membrane 101 and anion exchange membrane 102 is filled with a mixed ion exchange resin 103 of cation and anion exchange resins to form a desalination chamber 104. Moreover, portions formed by the anion and cation exchange membranes 102, 101 positioned adjacent to the desalination chambers 104 and not filled with the mixed ion exchange resin 103 are formed as concentrating chambers 105 for passing concentrated brine.
Moreover, as shown in FIG. 6, the cation exchange membrane 101, anion exchange membrane 102, and mixed ion exchange resin 103 (omitted from FIG. 6) filling the inside form a deionizing module 106.
Specifically, the cation exchange membrane 101 is sealed/attached on one side of a hollowed frame 107, the hollowed portion of the frame 107 is filled with the mixed ion exchange resin 103, and subsequently, the anion exchange membrane 102 is sealed/attached in the other side of the frame 107. Additionally, since the anion exchange membrane 102 is relatively soft, in general, a plurality of ribs 108 are vertically provided in the hollow space of the frame 107 in order to prevent the ion exchange membrane from being curved and prevent the layer filled with mixed ion exchange resin 103 from becoming non-uniform, when the inside of the frame 107 is filled with the mixed ion exchange resin 103 and opposite surfaces thereof are sealed with the ion exchange membranes.
Moreover, although not shown in the drawings, a feed water flow inlet is formed in an upper portion of the frame 107, while a deionized water flow outlet is formed in a lower portion thereof.
FIG. 5 shows that a plurality of deionizing modules 106 are arranged in parallel via spacers (not shown) disposed therebetween, a cathode 109 is disposed on one end of the arranged deionizing modules 106, and an anode 110 is disposed on the other end. Additionally, a space between the deionizing modules 106 disposed in parallel via the spacer is a concentrating chamber 105. Moreover, cation exchange membranes, anion exchange membranes, simple diaphragms having no ion exchange property or other compartment membranes 111 are disposed on opposite external sides of both end concentrating chambers 105 as required, and portions compartmentalized by the compartment membranes 111 and contacting both electrodes 109, 110 are formed as a cathode chamber 112 and anode chamber 113.
When deionized water is produced by the electrodeionization water producing apparatus, operation is performed as follows:
Specifically, a direct current voltage is applied between cathode 109 and anode 110, feed water flows in via a feed water flow inlet A, concentrated brine flows in via a concentrated brine flow inlet B, and electrode liquid flows in via electrode liquid flow inlets C and D. The feed water that flows in via the feed water flow inlet A flows downward in each desalination chamber 104 as shown by solid lines and arrows, and is passed through the filling layer of the mixed ion exchange resin 103, in which impurity ions are removed, and the deionized water is obtained via a deionized water flow outlet a. Moreover, the concentrated brine that flows in via the concentrated brine flow inlet B flows downward in each concentrating chamber 105 as shown by dotted lines and arrows, receives the impurity ions moving via both ion exchange membranes, and is discharged as the concentrated brine with the impurity ions concentrated therein via a concentrated brine flow outlet b. Furthermore, the electrode liquid that flows in via the electrode liquid flow inlets C and D is discharged via electrode liquid flow outlets c and d.
Since the impurity ions in the feed water are electrically removed, and concentrated in the concentrated brine by the operation described above, the deionized water can continuously be obtained without regenerating the filled ion exchange resins with chemicals.
When the conventional electrodeionization water producing apparatus is used, a reverse osmosis membrane device or a water softening device is usually installed as a pretreatment stage, so that the deionized water for use in various industries is supplied extremely effectively.
However, the conventional electrodeionization water producing apparatus has a complicated structure, and requires considerable time and labor to manufacture. Especially, the deionizing module forming the desalination chamber uses the frame with a plurality of ribs arranged in the hollow space to assure the filling of ion exchangers and uniform filling, which causes a problem that the configuration of the apparatus is restricted.
Therefore, an object of the present invention is to provide an electrodeionization water producing apparatus which maintains a deionizing efficiency as in a conventional case, has a simple structure, is easy to be manufactured and which has a high degree of freedom of apparatus configuration.
In such circumstances, the present inventor went back to a deionizing principle in an electrodeionization water producing apparatus, conducted a various studies and, as a result, has acquired the following information:
(1) A desalination chamber is filled with ion exchangers, i.e., ion exchange resins for the purpose of adsorbing ions in feed water. On the other hand, an ion exchange membrane is used for the purpose of transferring the ions adsorbed by the ion exchange resin to a concentrating chamber, and not transferring opposite ions of the concentrating chamber to the desalination chamber. Although the ion exchanger and the ion exchange membrane are different in purpose from each other, materials are substantially the same.
(2) When operation is performed without filling the ion exchange resins, the deionizing efficiency is remarkably deteriorated.
(3) Water electrolysis easily occurs in a portion where the ion exchange membrane and ion exchange resin come into contact with each other, and H+ or OHxe2x88x92 ions generated by the water electrolysis can be expected to chemically regenerate the ion exchange resin.
From the above (1) to (3), it has been found that when the desalination chamber is constituted by holding a channel for passing the feed water and allowing the cation exchange membrane to contact the anion exchange membrane, the same deionizing efficiency as in the conventional electrodeionization water producing apparatus can be obtained and an apparatus with a simple structure that is easy to manufacture and having a high degree of freedom of apparatus configuration can be obtained, and the present invention has been completed.
That is to say, according to the present invention, there is provided an electrodeionization water producing apparatus in which cation and anion exchange membranes are alternately arranged between an anode and a cathode, and desalination and concentrating chambers are alternately formed between both the membranes, the desalination chamber being formed by holding a channel for passing feed water from one to the other side of the desalination chamber and bringing the cation and anion exchange membranes into contact with each other.